基金The project supported by K.C. Wong Magna Fund in Ningbo University, National Natural Science Foundation of China under Grant Nos. 10747141 and 10735030;Zhejiang Provincial Natural Science Foundations of China under Grant No. 605408;Ningbo Natural Science Foundation under Grant Nos. 2007A610049 and 2006A610093;National Basic Research Program of China (973 Program 2007CB814800);Program for Changjiang Scholars and Innovative Research Team in University (IRTO734)